Photographic typesetting is commonly and conventionally used in the graphic arts industries as a technique for generating lithographic impressions.
So far as now known, the making of lithographic plates by a xerographic process using an ultraviolet light (UV) absorbing toner and a UV photosensitive plate has not been successful. A conventional xerographic toner powder, such as commonly employed in xerographic office document copying equipment, cannot readily be used for these purposes because dry toners contain a low concentration of pigment. Thus, their optical densities are too low to provide an effective contact mask when an intensive UV source is being used for imaging. Furthermore, the making of a xerographic high contrast negative mask in conventional lithographic photomaking processes requires efficient transfer of large solid areas which is difficult to achieve without pinholes or other defects.
These problems become acute when color reproductions are contemplated. Multiple separation transparencies must be prepared and used to prepare different lithographic plates for each color.
Lithographic plate making requires a toner which will provide a high transmission density to prevent defects in plates caused by light penetration through toned areas in a transparency. Thus, new toners and processing techniques are needed to manufacture transparencies suitable for use in making lithographic plates.